The regulation of interferon induction and synthesis will be studied in human diploid cells in cultures stimulated with polyinosinate-polycytidylate (poly I.poly C). To determine the concentration of active interferon messenger RNA (mRNA) in the cells at different times after induction, RNA will be extracted from cells, partially purified, and injected into Xenopus laevis oocytes. Interferon synthesis by the oocytes will be measured after appropriate incubation. This system will be utilized to study the validity of the "repressor hypothesis", stating that interferon synthesis is under negative control of a "repressor system" which is induced coordinately with interferon and which causes irreversible inactivation of interferon mRNA. Studies on the interaction of interferon with target cells will be continued, with the aim of characterizing the "interferon receptor" at the cell surface. New approaches will be developed for the study of the role of endogenous interferon in single-and multi-cycle infections with different viruses in cell cultures.